Gear induced noise in rotorcraft typically exceeds 100 dB, making it impossible to communicate without headsets. This has limited the use of rotorcraft for civilian transportation. The rotorcraft driveline system includes several sets of gears, which generate high frequency vibration as the gear teeth make contact. Once this vibration exits the driveline, it transfers to the passenger cabin and generates structure borne noise.
Further, the mechanical connections to the driveline system are responsible for suspending the passenger cabin in the air. These connections are critical, and therefore, soft isolation mounts cannot be employed to prevent the vibration transfer. Vibration damping and noise barriers on the cabin walls would be effective, but require more mass than is allowable for this type of aircraft. In this situation, reducing vibration within the driveline has proven to be the most viable option.
Currently, the most effective driveline modifications have been to redesign the gear tooth profiles and surface features. By making these changes, the transfer of motion through the gears has become smoother and hence less vibration is generated. This has led to global reductions in vibration and structure borne noise.
However, gear tooth modifications have not eliminated the problem. Noise in rotorcraft is still overwhelming, requiring the use of headsets for communication and creating an environment that prevents widespread use of rotorcraft for civilian transportation.
Thus, an alternative approach to solving this problem may be beneficial.